Fabrication of a composite of hydrated iron oxide and hydroxide via thermal hydrolysis for sugar decolorization

An iron-based hydrolyzate material was prepared with a thermal-hydrolysis method for the removal of colorants in sugar. The decolorization rate and sucrose recovery reached 94.2% and 97% with negligible Brix decrease. The adsorption selectivity for colorants reached 31.4 in the presence of sucrose. The processing capacity reached 274.7 g raw sugar/g Fe/h, and the quality of product met the requirement of the color standard of white sugar. The decolorization rates for brown sugar, melanoidin, and caramel reached 78%, 87%, and 95%, respectively. The composition of the hydrolyzate probably followed (Fe3O4)x·(FeOOH)y·Fe(OH)3·(H2O)24 (x and y are much smaller than 1). The affinity of this adsorbent for the colorants was proven by FTIR and XPS. The adsorption process followed pseudo-second-order kinetics and agreed with Langmuir and Temkin isotherm models. In the later stage, the adsorption process was limited by intraparticle diffusion resistance. This adsorption process was exothermic along with entropy decrease and spontaneity. The colorant-removing effect depended on the electrostatic attraction and coordination interaction between Fe2+ ions on the hydrolyzate and colorant anions. The spent hydrolyzate could be incompletely regenerated via elution with NaOH.